Katharine Trendacosta wrote a post called Why Expanded Universes Are Important. I agree with the basic idea, but not all the details. Trendacosta looks at a handful of reasons why tie-ins are good things.

The Expanded Universe as a Gateway to Science Fiction Reading. It works for some people, but I’ve encountered too many people who read tie-ins and find “real” SF uninteresting, and SF fans who sneer at tie-ins. Personally, I got into them more or less simultaneously, for different reasons.

Expanded Universes as Gateways to Fandom. Sure, to an extent. But I was a dedicated tie-in reader for a long time in isolation. The Internet was a more important route to fandom for me.

Expanded Universes as Gateways to Writers and Writing. Well, blogging, maybe. I’ve never been a fanfic writer. Closest I came was working on an interactive Star Trek story in Apple Basic on my old Apple ][+ many years ago. It wad fun, mapping out paths, giving a hypothetical player some choices that led in different directions… but I hit the 128k barrier way too early in the story and couldn’t figure out how to get each strand of the story to continue properly on the next program. Fun while it lasted, though. (Post-TMP Enterprise encounters a huge derelict starship that turns out to be a Preserver vessel. Didn’t plot it much beyond that that I can recall.)

Conclusion and a Look at Star Wars’ EU. In which Trendacosta basically says I love the Star Wars expanded universe and it was CANON! Well, actually, no. Despite the people with full-time jobs sorting out EU continuity, despite the levels of canonicity, George Lucas clearly said that there was his stuff and then there was all that other stuff he didn’t pay much attention to. In other words: NOT CANON. (And the correct response is Says you, and who cares?)

Here’s what makes tie-in fiction important and necessary and sometimes so damn good. When you see a filmed version of a beloved literary work, chances are, even if you like it you’re well aware of how much is missing — the interior lives of the characters, the background information that was dropped because the movie would run too long, scenes dropped because they just wouldn’t work in a visual medium. Play that in reverse. A good tie-in novel takes a visual world and expands it into an ocean of words that can bring us into characters’ interior lives as the show never could; they can show us all the little things that don’t make sense in a fast-paced movie or TV episode; they can be crazy big epic beyond a budget’s ability to realize. Try to imagine Doctor Who doing something like Alien Bodies or Star Trek doing something like Destiny (or How Much for Just the Planet, for that matter). It wouldn’t work as well on screen.